Towed agricultural implements, e.g., plows and the like, are attached to a tractor using what is known as a 3-point hitch. The hitch has a pair of laterally-spaced draft arms which can be raised and lowered to vary the height of the implement with respect to the surface of the ground. A third arm (sometimes referred to as an upper link or a center link) is above and laterally midway between the draft arms. Like the draft arms, the third arm also has an eye to attach to the implement being towed.
There are several reasons why it is desirable to be able to vary implement height and to hold the selected height, notwithstanding external, ground-imposed forces which may act on the implement. As an example, when a field is being tilled, it is preferred that the tillage implement engage the ground to the same depth for each "pass" of the implement through the field and to the same depth with respect to the entirety of any particular pass. And a field is often prepared to have a tilled portion for crop growing and non-tilled "headlands" at either of two opposed field boundaries. The headlands, covered with weeds, grass or the like, are usually at a somewhat higher elevation than the tilled portion. When the tractor and implement reach the end of a pass at a headland, the implement is raised to "clear" such headland while the tractor is making a U-turn into the next pass.
It is apparent from the foregoing that a characteristic of a conventional 3-point hitch is that once the vertical position of the hitch draft arms (and of the implement attached to the draft arms) is established, such position cannot be modified except by changing the vertical position of the draft arms. But workers in this area of technology have long recognized that there are times when it is desirable to let the implement "float," i.e., to seek its own elevation (within limits) under the urging of external forces as the implement is towed along and without moving the position of the lift links. And as the corollary, there are other times (in fact, most of the time) when it is desirable to prevent the implement from moving vertically except by controlling the height of the draft arms conventionally by moving the lift links.
For example, U.S. Pat. No. 3,380,759 (Engelmann) discloses a tractor draft arm support that has a link, one end of which is pivotally pinned to a draft arm. A midpoint of the link is pivotally pinned to a bifurcated support. In the "no-float" configuration, a rotatable lock pin engages the other end of the link and prevents link pivoting. In the float position, the lock pin is disengaged from such other end and the link is free to pivot about the midpoint pin. The draft arm is therefore free to move a limited distance and direction without moving the draft arm support.
U.S. Pat. No. 3,357,720 (Kulhavy et al.) discloses an apparatus which permits or prevents vertical float and horizontal sway. Vertical float is permitted or prevented by the position of a locking tongue with respect to an arm. The locking tongue slides into (no-float) or out of (float) engagement with such arm.
U.S. Pat. No. 1,574,351 (Altgelt) discloses a draft device having a draft member pinned to a coupling having diverging opposed sides. When a blocking pin is in place, the draft member is prevented from pivoting with respect to the coupling. But when the blocking pin is removed, the draft member is free to pivot within limits established by the diverging opposed sides. It is fair to say that the Altgelt device is not well suited for use with a modern 3-point hitch.
While these earlier devices have been (or were) generally suitable for the intended use, they are not without disadvantages. For example, the Engelmann, Kulhavy et al. and Altgelt devices all permit free pivoting movement but do not permit linear movement. And the Kulhavy et al. apparatus has a significant number of parts and some of those parts are, seemingly, closely-fitted to one another. A multiplicity of parts has adverse implications for cost and purchase price and, very possibly, for reliability. And closely-fitted parts are seemingly not well advised for use in applications (like implement towing) where dust, dirt, grime and water are common.
A new implement-positioning apparatus with improved float/no-float mechanism would be an important advance in the art.